Acetabular protrusion following endoprosthetic hip surgery: a multifactorial study.

Acetabular protrusion was found in 56 out of 211 patients fitted with a hemiprosthesis. The indication for operation was acute femoral neck fracture or failure following a previous internal fixation. A number of radiological variables were analysed with respect to their possible association with preoperative, operative and follow-up variables. After a preliminary screening of variables a deeper analysis was performed by fitting log-linear models to the data. Our analysis showed that the development of protrusion has a significant association with follow-up time. A previous hip operation was also significantly associated with the development of protrusion. This may be an indication for total hip replacement in some patients who now receive a hemiprosthesis as a secondary operation. Acetabular protrusion was significantly associated with the development of postoperative pain, while the other clinical symptoms and signs lacked any direct association with protrusion. Although acetabular protrusion and loosening of the prosthetic stem showed a significant association the analysis indicated that pain was primarily due to protrusion.